2024ApJ...974..250A

The hydrogen recombination lines H30α, H40α, H42α, H50β, and H57γ and the underlying bremsstrahlung continuum emission were detected with ALMA in the bipolar nebula Mz3. The source was not spatially resolved, but the velocity profile of the H30α line shows clear indication of maser amplification, confirming previous reports of laser amplification in the far-infrared H recombination lines observed with Herschel Space Observatory. Comparison between the flux densities of the H50β, H40α, and H42α lines show overcooling, or darkness amplification by stimulated absorption (dasar effect) at the LSR velocity of about -25 km s^–1, which constrains the density of the absorbing region to about 10³ cm^–3. The H30α line, on the other hand, presents maser lines at LSR velocities of -69 and -98 km s^–1, which indicates ionized gas with densities close to 10⁷ cm^–3. Although the source of emission was not resolved, it was possible to find the central position of the images for each velocity interval, which resulted in a well defined position-velocity distribution.